Rubber thread and method of making same



July 11, 1939. K. R. SHAW RUBBER THREAD AI ID METHOD OF MAKING SAME,

Filed Dec. 28, 1938 I/I/II/II/III IIIIII/I/I/A ii 22 322 2222 2"..............-... 'IIIIIIIIIl/II/III I II Ill/ II III/IIIIIIIII/l Patented July 11, 1939 RUBBER THREAD AND' METHOD OF MAKING SAME Application December 28, 1938, Serial No. 248,026

9 Claims.

Some rubber threads are composed of two, and sometimes, but rarely, of more, parallel strands adhesively united together throughout their length. Usually the adhesion between the strands is of such a nature that the thread is not an integral structure, although to all ordinary intents and purposes the thread may be used exactly as though it were. However, if one strand breaks the rupture will not run through the adjoining strand o-r strands. Consequently, a thread of this nature is particularly valuable in fabrics which are to be subjected to sewing or similar operations likely to injure the thread. In some cases, also, one strand may be of a very different nature from the other. For example, one strand may be made of vulcanized rubber and the adjoining or companion strand may be of unvulcanized rubber. Such a thread is valuable as the core of a covered rubber thread, since the unvulcanized strand cooperates with the inner wrapping of the covering to prevent relative slippage of the covering and core.

In manufacturing rubber threads of these forms, the method heretofore practiced exclusively, so far as I have been able to learn, has been to unite two or more sheets or plies of rubber face to face, each of substantially the length of the thread to be made, then to wind the composite sheet so formed on a drum and to cut threads from this sheet in the usual way by means of a rotary disk cutter.

Serious objections to this method are the fact that the length of thread which can be cut from such a sheet is only slightly greater than the length of the sheet itself so that it is impossible to produce threads by this method of the long lengths desired in weaving, braiding, and similar operations. Moreover, while this method of cutting thread has long been known, no practical way has been devised for guiding the threads away from the cutting point in any orderly fashion so that they do not become entangled with each other. It is therefore, necessary after the cutting operation has been completed to untangle the entire mass of threads, and this operation usually is the largest single item of expense in the production of this material.

In my prior Patent No. 2,082,744 I have disclosed a method of cutting ordinary rubber thread which overcomes the objections above described and, in addition, presents the rubber threads in an assembled form which has many advantages in the subsequent operations in which the thread is used, such as Weaving, braiding, beaming, spooliug, or the like.

The present invention aims to improve the methods of making these plural strand types of rubber thread with a View to realizing in the manufacture of them essentially the same advantages obtained in the method disclosed in the patent above referred to and to produce threads of this type in the assembled forms which have been found so advantageous in the use of the common forms of rubber thread.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawing, and the novel features will be particularly pointed out in the appended claims.

In the drawing:

Figure 1 is a plan view showing an ass-embling step in the method of this invention;

Fig. 2 is a similar View illustrating the cutting step;

Fig. 3 is an edge View of a stack of rubber sheets or plies made in accordance with the process provided by this invention;

Fig. 4 is a sectional view, partly in elevation, illustrating, on a larger scale, the cutting step shown in Fig. 2;

Fig. 5 is a plan view showing one method of separating the plural strand rubber threads from each other;

Fig. 6 is a perspective view on a large scale showing a portion of one product embodying the invention; and

Fig. 7 is a similar View of another embodiment of the invention.

Assuming that the thread to be manufactured consists of a strand of vulcanized rubber with a much thinner strand of unvulcanized rubber united therewith, the preferred method of procedure, according to this invention, involves the assembly of plies 2 and 3, Fig. 1, composed, respectively, of vulcanized and unvulcanized rubher. The sheets from which these plies are cut may be made by any suitable method. Practically always both are worked into sheet form by calendering, and in this operation the thickness of the plies also is predetermined. From the sheets so made sections of approximately circular form may be cut by any suitable method, and these sections are placed one upon the other and pressed together. The inherent adhesiveness of the rubber is such that they will unite very firmly simply by being brought in contact, as just described, and then pressed together. If greater adhesion is desired it can be produced by the application of a very moderate temperature or by wiping the contacting faces of the sheets with naphtha prior to assembly.

A series of these composite sheets are made and subsequently they are assembled in. superposed relationship to form a stack, as shown in Fig. 3, only a portion of the edge of such a stack being there illustrated. For convenience, these composite sheets will be designated by the letter a. During this assembling operation, however, the surfaces of the unvulcanized plies 3 are dusted with talc, or some equivalent separating material, the greater part of this talc being. rubbed off before the sheets are stacked together. The sheets are all assembled with the unvulcanized plies facing up or down, so that each vulcanized ply will be in contact with an unvulcanized ply of the next adjoining sheet. The quantity of talc left between the sheets is so governed as to reduce the strong adhesion that otherwise would.

be produced between them and to control or limit that adhesion to the desired value. After the stack has been completed it is preferably compressed between plates sufiiciently to make all of the sheets adhere to each other throughout their areas and thus to consolidate and solidify the stack for the subsequent cutting operation.

Such a stack is shown in Figs. 2, 3 and 4 at B. It may be supported and cut by any of the methods disclosed in my patent above referred to, the method commonly used being to make the stack of annular form and to cut from the inner edge by means of a rapidly revolving disk cutter 4. During this cutting operation the stack is supported on a turn table 5, surfaced with a relatively thick layer 6 of unvulcanized rubber into which the edge of the disk knife 4 can out. As the cutting operation progresses, the stack and the knife are relatively fed axially at the rate necessary to produce a tape or ribbon of predetermined thickness, and the ribbon is guided away from the cutting point and wound on a drum or conducted into a suitable receptacle. Usually the only finishing operation required on it is that of drying to evaporate the water picked up by the ribbon during cutting.

If the ribbon has been made with reference to the requirements of a particular braiding, weaving, beaming, spooling, or like operation, the ribbon may be taken directly, in the condition in which it comes from the cutting and drying operations, to the machine in which it is to be used. As it is fed to that machine, it can be split into its constituent threads in any of the various ways disclosed in my patent above referred to, or in my pending application Ser. No. 142,417. The ribbon at this time appears approximately as shown at I in Figs. 5 and 6, and it may be split simply by running it through a comb 9 having teeth H) which cooperate with the direction of feed of the tape and the tension maintained on it to break the adhesive bonds which hold the threads 8 united in a ribbon form. Because the strength of these adhesive bonds is controlled by the dusting of talc between the sheets from which they are cut and is purposely made relatively weak as compared to the strength of the bonds which unite the strands of each thread together, the splitting of the ribbon in this manner does not materially disturb or weaken the structure of the individual threads. Fig. 6 shows the tape on a considerably enlarged scale.

The invention thus provides an entirely satisfactory method of making rubber thread of the type just referred to in the long lengths desired for commercial use, while at the same time avoiding the difficulties heretofore experienced in making thread of this character. When such a thread includes an unvulcanized strand, it introduces problems in the manufacturing process which also are minimized by the method just described. Furthermore, this method is considerably more economical than those heretofore used and it presents threads of this pluralstrand type in a tape or ribbon form which is far more convenient for the further use made of such threads than when they are out individually, as has been the prior art practice.

While a ribbon of this same form and construction can be made by combining larger plies to make composite sheets, and mounting them on the drum of a thread cutting machine of the old type with the sheets superposed in cylindrical sections, one on the other, and bonded together, as described in my patent above designated, it is considered far more preferable to make circular sheets and to build a stack from them, as above described. The whole process is simplified by this method, it can be performed more expeditiously and economically, and a further and very important advantage is that each ply can be given a more thorough inspection because of the fact that the area to be inspected is so much smaller. Thus pin holes or other flaws or imperfections in the plies can be detected at almost the first step of the process, and the danger of producing rubber thread containing such imperfections, therefore, can be substantially eliminated.

Rubber thread of the type comprising two vulcanized strands, each of approximately the same cross-sectional dimensions united securely to each other, can be made by essentially the method above described. A ribbon composed of such thread is shown in Fig. 7 at H and the individual threads are indicated at l2. This process differs from that above described merely in that the plies initially assembled to produce a sheet are of substantially the same kind and thickness. In uniting them care is taken to see that they do not weld together into a unitary structure, and an extremely light dusting only of talc is required for this purpose. In assembling these sheets to form a stack, the adhesion of the sheets to each other is controlled in the manner above described. Thus, after the ribbon has been cut, adjacent threads will be united by adhesive bonds which are relatively weak so that they can easily be broken to split the tape into its individual threads, but the strands of each thread will be united firmly to each other. These firmer bonds are not weakened to any material degree by the subsequent splitting of the ribbon into its component threads. In Fig. 7, as also in Fig. 6, the weaker bonds uniting the threads are indicated by the heavier lines, while the stronger bonds uniting the strands of the individual threads are indicated by considerably lighter lines.

Having thus described my invention, what I desire to claim as new is:

1. That improvement in methods of making composite rubber thread which consists in assembling a series of sheets of rubber in superposed relationship, producing a substantially stronger adhesion between certain of said sheets than between others, cutting simultaneously through said assembly of sheets while relatively feeding the cutting implement and the assembly to produce a ribbon composed of strands'cut from said respective sheets, the adhesion of said sheets to each other being so controlled that all of said strands will be held together during the normal handling of said ribbon but the strands cut from weakly united sheets can readily be pulled apart and the ribbon can thus be divided into threads composed of strands which are firmly united to each other.

2. That improvement in methods of making rubber thread which consists in assembling plies of rubber in face to face relationship to produce a composite sheet in which the plies are firmly united, assembling a series of said composite sheets in superposed relationship to form a stack, producing a controlled adhesion between the sheets of said stack, cutting simultaneously through said stack while relatively feeding the cutting implement and said stack to produce a ribbon composed of threads cut from said respec-- tive sheets with each thread composed of strands adhesively united throughout their length, the adhesion between said sheets being so controlled that the union between the threads cut from. them will be sufiiciently strong to maintain them in said ribbon form for normal handling but will permit them to be readily pulled apart while the adhesion of said strands to each other remains substantially undisturbed.

3. That improvement in methods of making rubber thread which consists in assembling two circular plies of rubber in superposed face to face relationship and under such conditions that they become firmly united due to the inherent adhesiveness of the rubber and form a composite sheet, assembling a series of said composite sheets in superposed relationship to form a circular stack, during the latter assembling operation introducing a sufiicient quantity of talc or equivalent separating material between the adjacent sheets to produce a controlled adhesion of the sheets to each other, subsequently cutting a ribbon from the edge of said stack by relatively revolving the stack and a cutting implement while relatively feeding the two radially at such a rate as to produce a ribbon of a predetermined thickness, and guiding the ribbon away from said cutting point, whereby the ribbon so produced will be composed of threads of plural strand form and said threads may readily be separated from each other by breaking the controlled adhesions uniting them.

4. That improvement in methods of making rubber thread which consists in assembling a circular ply of vulcanized rubber with a similar ply of unvulcanized rubber, with the two plies in face to face relationship, causing said plies to adhere firmly to each other and thus to produce a composite sheet of rubber, assembling a series of said sheets in superposed relationship to form a circular stack with the vulcanized ply of one sheet in contact with an unvulcanized ply of an adjoining sheet, during said assembling operation producing a controlled adhesion of the sheets of said stack to each other, subsequently cutting a ribbon of predetermined thickness from the edge of said stack so that said ribbon consists of plural strand threads cut from the respective sheets of which the stack is composed, said adhesion being so controlled that the threads of said ribbon will be united to each other with suflicient strength to maintain the integrity of the ribbon during normal handling but can readily be divided into its component threads by breaking the controlled adhesive bonds uniting the threads to each other.

5. An article of the character described comprising a series of rubber strands lying side by side and adhesively united to each other to form a ribbon, the adhesive union between said strands at regularly spacedintervals being weaker than the adhesive bonds joining the other strands together, so that said relatively weak bonds may be readily broken and the ribbon thereby divided into threads or strips each composed of a predetermined number of strands firmly united to each other.

6. An article of the character described comprising a series of rubber strands lying side by side and adhesively united to each other to form a ribbon, the adhesive bonds uniting said strands being of difierent strengths, strong bonds alternating with weak bonds, so that the weak bonds may readily be broken and the ribbon thereby divided into threads each composed of two strands firmly united to each other.

7. An article of the character described comprising a fiat, relatively wide ribbon composed of a series of rubber threads bonded directly to each other in parallel side by side relationship, each thread being composed of strands adhesively but not integrally united throughout their length, the adhesion between said strands of each thread being relatively permanent but the adhesion of the threads to each other being so reduced and controlled by an intervening separating substance that the ribbon may readily be split into its component threads merely by breaking the relatively weak bonds, the latter bonds, however, being sufiiciently strong to maintain the integrity of the ribbon during normal handling.

8. An article of the character described comprising a fiat, relatively wide ribbon composed of a series of rubber threads bonded directly to each other in parallel side by side relationship, each of said threads also being composed of strands adhesively united to each other in parallel side by side relationship, one at least of the strands of each thread consisting of vulcanized rubber and another of unvulcanized rubber, the union of said strands to each other holding them in a fixed relationship to each other substantially throughout the length of the thread, and the bonds between adjacent threads being relatively weak so that the ribbon may be divided into its component threads by breaking said weak bonds without materially weakening the adhesive union between the strands of the individual threads.

9. An article of the character described comprising a fiat, relatively wide ribbon composed of a series of rubber threads bonded directly to each other in parallel side by side relationship, each of said threads also being composed of strands adhesively united to each other in parallel side by side relationship, one at least of each of the strands of each thread consisting of vulcanized rubber and another of unvulcanized rubber, the union of said strands to each other holding them in a fixed relationship to each other substantially throughout the length of the thread, the threads being united to each other by the adhesion of an unvulcanized strand of one thread to a vulcanized strand of an adjoining thread, and the bonds holding said threads together in their assembled relationship being relatively weak so that they may be readily broken and the ribbon thereby divided into its component threads without materially weakening the structure of the individual threads.

KENNETH R, SHAW. 

